1. Field of the Invention
The present invention relates to driving force controlling apparatus and method for a four-wheel drive vehicle.
2. Description of the Related Art
A previously proposed driving force controlling apparatus for the four-wheel drive vehicle is exemplified by a Japanese Patent Application First Publication No. Heisei 7-172204 published on Jul. 11, 1995.
In the previously proposed driving force controlling apparatus disclosed in the above-described Japanese Patent Application First Publication, road wheel velocity sensors detect respective road wheel velocities, determines a difference in the road wheel velocities between front and rear road wheels (hereinafter, referred to as a front-and-rear road wheel velocity difference), determines a variation rate of the front-and-rear road wheel velocity difference, and sets a driving force distribution between the front and rear road wheels according to the front-and-rear road wheel velocity difference and its variation rate. That is to say, the vehicle in which the above-described driving force controlling apparatus is mounted falls in a four-wheel drive state only when at least one of rear left and right road wheels develops an acceleration slip and the front-and-rear road wheel velocity difference occurs.
However, since, in the above-described driving force controlling apparatus for the four-wheel drive vehicle, the vehicle does not fall in the four-wheel drive state unless the front-and-rear road wheel velocity difference is generated, it is impossible to run continuously under the four-wheel drive state in order to secure a running stability and a running through performance in a case where the four-wheel drive vehicle is running on a slippery low frictional coefficient (xcexc) road surface or a rough road. In addition, since, in the previously proposed driving force controlling apparatus described above, main driven wheels are in a slippage state at a time of the four-wheel drive state, there is no margin in a gripping force on the main driven wheels and it is not preferable with a vehicular stability taken into consideration. Furthermore, in the above-described previously proposed driving force controlling apparatus, there may be a case where four-wheel drive state and two-wheel drive state are repeated on the road surface having a low frictional coefficient xcexc. In this case, an unpleasant feeling may be given to the vehicular driver due to variations in a vehicular acceleration and vehicular velocity caused by a mechanical loss and an electrical loss during the four-wheel drive state.
It is, hence, an object of the present invention to provide driving force controlling apparatus and method for the four-wheel drive vehicle which can cause the vehicle to run continuously under the four-wheel drive condition only during an occurrence of its necessity.
According to one aspect of the present invention, there is provided a driving force controlling apparatus for a four-wheel drive vehicle, comprising: main driven wheels which are one of front and rear road wheels; auxiliary driven wheels which are the other of the front and rear road wheels; a slip detecting section that detects an acceleration slip quantity of the main driven wheels; a driving force demand determining section that determines whether there is a vehicular driver""s demand on the driving force; an auxiliary driven wheel driving force distribution rate maximum value updating section that calculates a driving force distribution ratio between the front and rear road wheels in such a manner that a driving force distribution rate for the auxiliary driven wheels is updated to its maximum value on the basis of the slip quantity of the main driven wheels detected by the slip detecting section when the driving force demand determining section determines that there is the vehicular driver""s demand on the driving force; a slip responsive driving force distribution ratio calculating section that calculates the driving force distribution ratio between the front and rear road wheels in accordance with the acceleration slip quantity when the driving force demand determining section determines that there is no vehicular driver""s demand on the driving force; and a driving force adjusting section that adjusts variably the driving force between the front and rear road wheels in such a manner that the driving force distribution ratio between the front and rear road wheels indicates that calculated by at least one of the auxiliary driven wheel driving force distribution rate maximum value calculating section and the slip responsive driving force distribution ratio calculating section.
According to another aspect of the present invention, there is provided a driving force controlling apparatus for a four-wheel drive vehicle, comprising: driving force controlling apparatus for a four-wheel drive vehicle, comprising: main driven wheels which are one of front and rear road wheels; auxiliary driven wheels which are the other of the front and rear road wheels; a slip detecting section that detects an acceleration slip quantity of the main driven wheels; a driving force demand determining section that determines whether there is a vehicular driver""s demand on the driving force; an auxiliary driven wheel driving force distribution rate maximum value updating section that calculates a driving force distribution ratio between the front and rear road wheels in such a manner that a driving force distribution rate for the auxiliary driven wheels is updated to its maximum value on the basis of the acceleration slip quantity of the main driven wheels detected by the slip detecting section when the driving force demand determining section determines that there is the vehicular driver""s demand on the driving force; an auxiliary driven wheel driving force distribution rate reducing section that calculates the driving force distribution ratio between the front and rear road wheels in such a manner that the driving force distribution rate for the auxiliary driven wheels is reduced or zeroed when there is no vehicular driver""s demand on the driving force; and a driving force adjusting section that adjusts variably the driving force between the front and rear road wheels in such a manner that the driving force distribution ratio between the front and rear road wheels indicates that calculated by at least one of the auxiliary driven wheel driving force distribution rate maximum value calculating section and the auxiliary driven road wheel driving force distribution rate reducing section.
According to a still further aspect of the present invention, there is provided a driving force controlling method for a four-wheel drive vehicle, the four-wheel drive vehicle including main driven wheels which are one of front and rear road wheels; and auxiliary driven wheels which are the other of the front and rear road wheels, the driving force controlling method comprising: detecting an acceleration slip quantity of the main driven wheels; determining whether there is a vehicular driver""s demand on the driving force; calculating a driving force distribution ratio between the front and rear road wheels in such a manner that a driving force distribution rate for the auxiliary driven wheels is updated to its maximum value on the basis of the slip quantity of the main driven wheels detected by the slip detecting section when determining that there is the vehicular driver""s demand on the driving force; calculating the driving force distribution ratio between the front and rear road wheels in accordance with the acceleration slip quantity when determining that there is no vehicular driver""s demand on the driving force; and variably adjusting the driving force between the front and rear road wheels in such a manner that the driving force distribution ratio between the front and rear road wheels indicates that calculated at least one of such a manner that a driving force distribution rate for the auxiliary driven wheels is updated to its maximum value and such a manner as calculated in accordance with the acceleration slip quantity.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.